A retrieval catheter is disclosed in WO-A-01/12082. The catheter can be used to retrieve an embolic filter from the vasculature. It features an elongate flexible tube which has a radially expansible distal tip with an open mouth for retrieval of the filter. A centering catheter is used to centralize the retrieval catheter within the vasculature. This enables the retrieval catheter to pass freely through a stenosis or a stent to retrieve a filter.
The present Applicant has disclosed in WO-A-01/34061 a catheter device for delivering an implant, particularly a self-expanding stent. The catheter has an atraumatic distal tapered tip and a lumen just proximal of the tapered tip in which a self-expanding stent is carried. Just proximal of the stent so carried is a pusher ring which abuts the proximal end of the compressed stent within the lumen. For delivery of the stent, the pusher is held in the desired stent delivery disposition within the bodily lumen, and the catheter tube is pulled proximally backwards over the length of the stent, with the distal tip stretching as is slides over the abluminal wall surface of the stent and thereby progressively releases the stent for expansion into the bodily lumen, starting at the distal end of the stent, and continuing progressively and steplessly towards the proximal end of the stent.
As explained in WO-A-01/34061, there are stenting procedures in which it is preferred or essential to place a protection device distal of the stenting site, before the stenting procedure commences. For example, when placing a stent in the carotid artery, it is vital to ensure that plaque displaced from the artery wall by the placement of the stent is not entrained in the vascular fluid and carried along the carotid artery to the brain. To prevent any such adverse occurrence, it is customary to place in the carotid artery, distal of the stenting site, either an inflated balloon which occludes the artery, or a mesh filter which catches any debris dislodged by placing the stent.
Of course, once the stent has been successfully placed, there is the need to remove the protection device, and this is customarily done by withdrawing the protection device through the stent lumen. It will be appreciated that the stent lumen might itself not be entirely free of debris, or bodily tissue protruding radially inwardly into the stent lumen through the expanded mesh openings of the stent after it has been expanded and put in place in the artery. Clearly, all the protections against escape of debris during the stenting procedure counts for nothing if withdrawal of the protection device itself releases debris which remains uncaptured.
Accordingly, there is a need for protection devices which can be withdrawn through the lumen of a placed stent with reduced or minimized likelihood of displacement of bodily tissue such as plaque during withdrawal of the placement device through the stent lumen.
Evidently, what is needed is a retrieval system for the protection device that will minimize the possibility for steps or edges or discontinuities on the surface of the device from snagging or scraping or dragging across any surface where debris might be released. In other words, just as the distal tip of a distally advancing catheter should be as atraumatic as possible, so should all surfaces of a protection device and its associated retrieval catheter, when being withdrawn proximally away from its operational site and through the lumen of a previously placed stent.
However, the requirement for an atraumatic tip on a retrieval catheter to be advanced distally into a bodily lumen, and a configuration for proximal withdrawal that is also devoid of discontinuities, is not obvious. In particular, a retrieval catheter with an atraumatic distal tip that tapers to a point is hardly adapted to create, in combination with the device to be retrieved, a system devoid of any discontinuities or surfaces that might snare, snag or scrape any surface of the stent through which the system is to be proximally withdrawn.
In this specification, priority is claimed, from British Patent Application No. 0323971.2. In that application the British Patent Office performed a patentability search and listed the following publications on its second report: U.S. Pat. No. 5,868,753; 2002/0010476; 2002/0058963 and 2002/0183781, as well as EP-A-1232765. However, it allocated all of these references only to category A—technological background.
For further disclosures of catheters to retrieve a distal protection device, see WO 98/39053.